The present invention relates to a mask and a vent assembly therefor.
The mask and vent assembly according to the invention have been developed primarily for the venting of washout gas in the application of continuous positive airway pressure (CPAP) treatment in conjunction with a system for supplying breathable gas pressurised above atmospheric pressure to a human or animal. Such a system is used, for example, in the treatment of obstructive sleep apnea (OSA) and similar sleep disordered breathing conditions. However, the invention is also suitable for other purposes including, for example, the application of assisted ventilation or respiration.
The term xe2x80x9cmaskxe2x80x9d is herein intended to include face masks, nose masks, mouth masks, nasal pillows, appendages in the vicinity of any of these devices and the like.
Treatment of OSA by CPAP flow generator systems involves the continuous delivery of air (or other breathable gas) pressurised above atmospheric pressure to a patient""s airways via a conduit and a mask.
For either the treatment of OSA or the application of assisted ventilation, the pressure of the gas delivered to a patient can be at a constant level, bi-level (ie. in synchronism with patient inspiration and expiration) or autosetting in level to match therapeutic need. Throughout this specification the reference to CPAP is intended to incorporate a reference to any one of, or combinations of, these forms of pressure delivery.
The masks used in CPAP treatment generally include a vent for washout of the gas to atmosphere. The vent is normally located in the mask or in the gas delivery conduit adjacent the mask. The washout of gas through the vent is essential for removal of exhaled gases from the breathing circuit to prevent carbon dioxide xe2x80x9cre-breathingxe2x80x9d or build-up, both of which represent a health risk to the mask wearer. Adequate gas washout is achieved by selecting a vent size and configuration that will allow a minimum safe gas flow at the lowest operating CPAP pressure, which, typically can be as low as around 4 cm H2O for adults and 2 cm H2O in paediatric applications.
Prior art masks are generally comprised of a rigid plastic shell which covers the wearer""s nose and/or mouth. A flexible or resilient rim (or cushion) is attached to the periphery of the shell which abuts and seals against the wearer""s face to provide a gas-tight seal around the nose and/or mouth.
A prior art washout vent utilized one or more holes or slits in the rigid shell or in a rigid portion of the delivery conduit to allow the washout gas to vent to atmosphere. In some masks, the holes or slits were formed during the moulding process. In others, they were drilled or cut as a separate step after the shell or conduit had been moulded.
The flow of gas out the holes or slits in the shell or conduit to atmosphere creates noise and turbulence at the hole or slit outlet as the delivered gas, and upon expiration, the patient-expired gas (including CO2) exits. Bi-level and autosetting gas delivery regimes tend to generate more noise than a constant level gas delivery regime. This is thought to be due to the extra turbulence created by the gas accelerating and decelerating as it cycles between relatively low and relatively high pressures. The noise adversely affects patient and bed-partner comfort.
Another prior art vent included hollow rivets or plugs manufactured from stainless steel or other rigid materials attached to openings in the rigid shell. The outer edges of the rivets were rounded to help reduce noise. However, this approach was expensive, required an extra production step and did not prove effective in reducing noise.
Another approach to reduce noise involved the use of sintered filters at the gas outlet of the mask shell. However, the filters were prone to blocking, especially in the presence of moisture. Accordingly, sintered filters were impractical for use in CPAP treatment as they were easily blocked by the moisture from the patient""s respiratory system or humidifiers or during the necessary regular cleaning of the mask and associated componentry.
Foam filters wrapped around the air outlets in the shell were also attempted. However, they also suffered from the disadvantages of being prone to blocking, difficult to clean and requiring constant replacement.
Remote outlet tubes have been used to distance the noise source from the patient. However, these tubes are difficult to clean, are prone to entanglement by the patient and/or their bed partner and suffer the further disadvantage that a volume of exhausted gas is retained in the tube adjacent the mask.
It is an object of the present invention to substantially overcome or at least ameliorate the prior art disadvantages and, in particular, to reduce the noise generated by gas washout through a mask.
Accordingly, the invention, in a first aspect, discloses a mask for use with a system for supplying breathable gas pressurised above atmospheric pressure to a human or animal""s airways, the mask includes a mask shell which is, in use, in fluid communication with a gas supply conduit, a gas washout vent assembly, wherein at least the region of the mask shell or conduit surrounding or adjacent the vent assembly is formed from a relatively flexible elastomeric material.
In an embodiment, the entire mask is formed from the elastomeric material.
In another embodiment, the mask shell and/or conduit is formed from a relatively rigid material and the region surrounding or adjacent the vent assembly is formed from the relatively flexible elastomeric material.
In a second aspect, the invention discloses a vent assembly for the washout of gas from a mask or conduit used with a system for supplying breathable gas pressurized above atmospheric pressure to a human or animal, wherein the vent assembly is formed from the relatively flexible elastomeric material.
In a preferred embodiment, the vent assembly is an insert of relatively flexible elastomeric material, wherein the insert is attachable to the mask shell or conduit. The insert preferably has at least one orifice therethrough.
In a preferred form, the rigid plastics mask shell is formed from polycarbonate and the insert is formed from Silastic(trademark) or Santoprene(trademark).
Desirably, the insert is substantially crescent-shaped and includes a plurality of orifices therethrough.
The insert preferably includes a groove around its periphery, the groove adapted to locate the insert against a correspondingly sized rim of an opening formed in the mask shell or conduit.
In other embodiments, the insert is substantially circular, triangular, cross or peanut shaped.
The mask shell and/or the conduit can desirably also include one or more inserts.